In Yahoo answer account should not be suspended but points should be deducted in case of breach of "DECENCY"?

No, I don't think that would help matters, because points really don't mean much and taking them away does absolutely nothing to stop somebody from continuing to post offensive stuff. Besides, people should have a clear idea what sort of things would be considered indecent, so I don't have much sympathy for them if they get suspended.

I am wondering since year, is it decency on part of yahoo answer team to allow business promotion questions like call girls available-escort services available at so and so places?

This reminds me “Boss is always right”

The rules are clear and we agreed to them. Break the rules and you get suspended. Yahoo make the rules and they are happy with them so it is not for us to alter them.